It was to Nicolas Bion, map and globe maker of Paris that the astronomer Cassini entrusted the manufacture of such an instrument, and it is from him that we have a brief description of its peculiar features.[129] He tells us that the sphere on which the several constellations were represented was enclosed within a number of armillae representing the celestial circles, that is, the colures, the ecliptic, the tropics, the equator, and the polar circles. This inner sphere was attached to a meridian circle at the poles of its equator, within which circle it turned as the ordinary sphere, and it was also attached to the same meridian at the poles of the ecliptic. Around this polar axis of the ecliptic the sphere, with the attached meridian, could be made to revolve, the pole of the equator in its revolution tracing a circle having a radius of twenty-three and a half degrees, a complete revolution being made to represent a period of twenty-five thousand two hundred years, or the time required for the complete precession of the equinox according to his reckoning. This pole in its circle of revolution could be immovably set at any desired point to represent any time past or future, and the sphere then revolved around the pole of the equator. The several stars or constellations could thus be represented in their proper position for the time selected. Bion’s reference to this globe seems to assure us that he completed its construction, yet no trace of it has been left, unless we have such in a record to be found in the history of the Royal Academy for the year 1727. In this we find that a globe constructed on the principle laid down by Cassini was presented to the Academy, in the year designated, by Outhier, a priest of Besançon.[130] This globe, which has disappeared, had the double movements, one about the axis of the equator and one about the axis of the ecliptic. It was a globe which would represent the daily and annual movements of the sun, the difference between the true and the mean time, the movements of the moon and its phases, the eclipses, and the passing of the several fixed stars across the meridian. [Illustration: Fig. 119. Portrait of Jean Dominique Cassini.] [Illustration: Fig. 123. Portrait of Nicolas Bion.]